This paper describes how to write programs that interface with the C UNIX operating system in a non-trivial way. This includes programs that use files by name, that use pipes, that invoke other commands as they run, or that attempt to catch interrupts and other signals during execution.

The document collects material which is scattered throughout several sections of The C UNIX Programmer's Manual .R [1] for Version 7 C UNIX . There is no attempt to be complete; only generally useful material is dealt with. It is assumed that you will be programming in C, so you must be able to read the language roughly up to the level of The C Programming Language .R [2]. Some of the material in sections 2 through 4 is based on topics covered more carefully there. You should also be familiar with C UNIX itself at least to the level of C UNIX for Beginners .R [3].